Abstract: A driving mechanism for a travelling toy automatically runs backwardly when its forward movement is hindered by an obstacle. The driving mechanism includes a rotatable sun gear which selectively drives a wheel shaft through either a first or second oppositely facing crown gears secured to the wheel shaft. A pivotal arm carrying an intermediate planetary gear effects drive through the sun gear and planetary gear to a selective crown gear in dependence on the position of the arm. The arm position is controlled by engageable steps and control dogs.